Synthesis of new bimetallic complexes as catalysts for α-olefin polymerization: A study theoretical and experimental

Full text: The present study aims at the synthesis of new post-metallocene catalysts for the production of polyolefins with specific properties. The study of the synthesis and application of homo or hetero bi-metallic catalysts for polymerization processes has attracted the attention of the international scientific community due to recent advances in the field, particularly by getting ultra molecular weight polyethylene. To carry out the work were synthesized and characterized 8 chelate ligands (N,O donors) capable of supporting two metal centers of Nickel(II); 8 bi-metallic complexes were prepared from these ligands. The class of ligands choosed for the synthesis of nickel bimetallic complexes is known in the literature as phenoxy-imines, molecules that coordinate to the metal center through phenolate and imino group. Using 2 eq. of a derivative of the salicylaldehyde with 1 eq. of the dianiline, it's possible to obtain a linker with two coordination sites capable of supporting two metal centers. The ligands were characterized by ¹H NMR, I.R spectroscopy, mass and elemental analysis, and complexes by IR, UV-Vis and M.P. In addition to the experimental study, we developed a theoretical study using DFT method by optimizing the structures of ligands, complexes, intermediates and transition states of energy in order to understand the mechanism of polymer reactions. The structures of the ligands and complexes have been optimized and their infrared absorption spectra compared to the experimental spectrum. The governing principles of the proposed mechanism are being established for the active species. 4 catalysts had its polymer activities tested so far producing different polyethylenes, characterized by X-ray diffraction, TGA and DSC. We observe a good agreement between theoretical and experimental data. (author)